The problem appears to be bad. Earlier today, in a reader poll, Engadget found that over 8,000 of their readers had noticed yellow banding or blotching on their new iPhone 4s. That was 38% of their polled iPhone 4 owners.

It looked like Apple had a big problem on its hands… a problem far bigger than the similar issue Apple had with yellow iMac displays.

However, there’s good news. The culprit of the yellowing appears to be the adhesive used, galled Organofunctional Silane Z-6011. And it goes away according to a source by Apple Insider.

Apple is using a bonding agent called Organofunctional Silane Z-6011 to bond the layers of glass. Apparently, Apple (or more likely Foxconn) is shipping these products so quickly that the evaporation process is not complete. However, after one or two days of use, especially with the screen on, will complete the evaporation process and the yellow “blotches” will disappear.

How do I know? I was involved in pitching Z-6011 to Apple

We’ll have to see if this proves true, but given how widespread the problem is, we certainly hope it is. Otherwise, Apple might have a mass recall on its hands.